An infra-red light-emitting diode (LED) is mainly used in the optical communication industry. However, as semiconductor laser diode (LD) technology matures, the light source using the LED such as infra-red light LED with a wavelength between 1310 nm and 1550 nm, originally used in glass optical fiber, has been replaced by LD gradually so as to increase transmission distance. Network connection in the family and the multimedia such as digital video primarily uses plastic fiber and red LED with a wavelength between 650 and 670 nm. Therefore, currently available application of infra-red LED is sensors, remote controllers, etc., which operates at a wavelength between 850 and 950 nm. At present, optoelectronic components, particularly light-emitting components, are manufactured by epitaxial technology using elements in III-V group or II-VI group with a direct band-gap in periodical table as the raw material.
Since the invention of the transistor in 1947, silicon has always played an important role in the integrated circuit industry. According to the prediction of the Moore's Law, the size of the integrated circuit device will shrink to half of the original size at an interval of about 18 months. The basis of the Moore's Law is the innovation of new technology and the development of potential applications, wherein silicon is an important milestone in this fast progress. With years of development, silicon is the most complete and inexpensive material used in the integrated circuit fabrication. Therefore, the light-emitting device can be integrated into the very large scale integration (VLSI) circuit if silicon can be further developed to serve as a light-emitting device.
At room temperature, silicon, an element of IV group in the periodic table, is an inefficient light-emitting source because it is one of the indirect band-gap materials with a very low radioactive recombination rate and an internal quantum efficiency of only about 10−6 to 10−7, so that silicon has not been used as a light-emitting source. As a result, silicon is only used in light receiving devices such as detector, charge coupled device (CCD), array type video sensor and solar battery in photoelectric industry.
In 1990, a British L. T. Canham found that porous silicon (PSi) generated by anode electrolysis of silicon in hydrofluoric acid solvent can emit a visible light at high efficiency (See: Canham L. T., Appl. Phys. Lett., 57, 1046 (1990)). This important discovery prompted research teams in many countries to develop the silicon light source. During 2000 to 2003, many academic research institutes and researchers all over the world participated in the development of a silicon-based LED and gained some great result (See: Mykola Sopinskyy and Viktoriya Khomchenko, Current Opinion in Solid State and Material Science 7(2003) 97–109.). However, there are so far still not any commercial optoelectronic products such as LED in spite of preferable result in research and development of silicon-based LED at present.
Due to the sponge-like structure, the porous silicon has some major defects in the application to the light-emitting device. As to the mechanical property, the porous silicon is inappropriate to be integrated with the standard semiconductor fabrication process for the frangibility of the former. In addition, the porous silicon is highly reactive in chemical properties and is likely to react with oxygen in the atmosphere, which results in the degradation of the photoelectric property. The degradation of the photoelectric property causes more difficulty in controlling the variation of the photoelectric properties with time.